Mining and construction machinery employ various implements, such as buckets, rams, forks, grapples, thumbs, etc., to perform different operations. These implements are commonly attached to the machine with a movable joint such as a pin joint, and are moved relative to the machine by actuators. When the operation that an implement performs is not needed, an operator may desire to move the implement into a stored, inactive position.
For example, when a bucket and a thumb is attached to the stick of a hydraulic excavator, the operator may use the thumb to assist in grabbing material, like tree stumps or demolition debris, by pinching the material with the thumb against the bucket. But when the thumb is not needed for grasping material or other operations, and the operator wishes to use the bucket to dig, the operator may wish to move the thumb to a stored, inactive position. The thumb may be moved to such a stored, inactive position by curling the thumb backwards until it folds against the stick.
An implement may be moved relative to the machine into the stored, inactive position primarily through force applied to the implement by the actuator. The actuator could be a hydraulic cylinder or a lead screw, as non-limiting examples.
Some types of actuators may be capable of moving an implement to its stored, inactive position, but may not be suitable for holding the implement in that position. For example, a hydraulic cylinder could be used to curl a thumb on an excavator stick backwards towards the stick. The thumb can be stored there, in an out of the way position, until the thumb is needed again. But the hydraulic cylinder may not be suitable for holding the thumb in that position. A hydraulic cylinder can drift over time because of leakage of hydraulic fluid around seals and valves. If the hydraulic cylinder drifts, the implement will be unintentionally moved from its stored position. The excavator operator may be required to correct the drift of the thumb by commanding a corrective movement of the hydraulic cylinder. Frequently correcting this drift can be tedious and distracting for the operator.
Latches are sometimes used to lock implements in their stored, inactive position by preventing drift. Various latches for this purpose have been used and proposed. One simple type of latch is a manual pin which pins the implement to the machine. To latch an implement with this type of latch, the operator of the machine is typically required to leave the cab, get into position next to the implement to be latched, and manually insert a pin between the implement and the machine. Manual pins are not attractive because of the time and effort required by the operator to insert the pin.
Other latches, such as the one proposed in U.S. Pat. No. 6,209,237, assigned to Rockland, Inc., are automatic latches which can latch and/or unlatch an implement without requiring the operator to leave the cab. The automatic latch illustrated in the Rockland patent permits automatic latching of a thumb on an excavator in a stored, inactive position. To automatically latch the thumb, the thumb is first moved to the stored position by a hydraulic cylinder or other actuator. Moving the thumb into the stored position causes the latch to automatically engage, and the thumb to be automatically latched in the stored position. Latching is automatic because it can be accomplished by the operator commanding movement of the thumb into the stored position from within the excavator's cab. In addition, the automatic latch illustrated in the Rockland patent can automatically unlatch the thumb from its stored position. To automatically unlatch the thumb, the operator commands the hydraulic cylinder to apply a force to the thumb to move it away from the stored position. The force from the hydraulic cylinder overcomes the latch's unlatching force causing it to automatically disengage, and the thumb to be automatically unlatched.
While the latch in the Rockland patent provides automatic latching and unlatching and works with certain thumbs, it is not well suited to work with other thumbs. For example, the manner in which the latch in the Rockland patent is positioned may limit the locations where the cylinder for positioning the thumb can be attached to the stick. Also, it may be difficult for the latch in the Rockland patent to achieve an unlatching force great enough for very large and heavy thumbs. In addition, while the latch in the Rockland patent provides automatic unlatching, it is difficult to manually unlatch it. Manual unlatching of the Rockland patent's latch can require a relative large amount of force and be difficult. Easy manual unlatching is appreciated by technicians who may need to manually disengage the latch to move the thumb during a servicing operation.
In contrast, the latch of the present invention is well suited to work with many different types of thumbs and other implements, by being flexible in the way in which it is positioned relative to the implement, and by being able to achieve a relatively high unlatching force so it can be used with large and heavy thumbs and other implements. The latch of the present invention is also simple to construct, install, and maintain, inexpensive, and easier to manually unlatch than other automatic latches.